Gas to gas counter-flow heat exchangers are well known. In particular, heat exchanger modules comprising a folded sheet of heat conductive material, the individual folds of the sheet defining adjacent fluid flow passages, wherein alternate ones of the passages define first conduit means for conducting relatively cool gases and wherein the other passages define second conduit means for conducting relatively warm gases, and a casing in which the folded sheet is contained, the casing having entrance and exit openings for each conduit means, are well known (See, for example, U.S. Pat. No. 2,019,351 to Lathrop). These heat exchanger modules have the common characteristic that the length of the flow path in each conduit means is significantly larger than at least one of the width dimensions of the flow path to minimize deleterious entrance effects.
Thus, should it be desired to increase the capacity of such a heat exchanger module, the width of the module must be increased since the maximum dimension of the depth is limited. However, even the width dimension of such a heat exchanger module is limited in that the space in which the module is to be installed is often limited. Even if the installation space does not impose such a requirement, increasing the width of a heat exchanger module often results in the module attaining awkward dimensions.
Thus there is a problem in the design of high capacity gas to gas counter-flow heat exchangers of the type described hereinabove.